The present invention relates to an optical pickup device used for reproduction and recording from/into an optical disk such as CD (compact disk), DVD (digital versatile disk), etc., and a connection structure of flexible printed circuits used in optical pickup devices.
Conventionally, a thin optical pickup device (having a thickness of at most 7 mm) used for reproduction and recording from/into an optical disk such as CD, DVD, etc., or an optical disk drive device with a thin optical pickup device incorporated therein is structured as shown in FIG. 8. Parts, such as laser diode, various lenses, mirror, photodetector (not shown), etc., which constitute an optical system, are arranged on an optical pickup case 3 formed by means of die casting or molding, of which main components comprise metal such as Zn, Mg, Al, etc. and a PPS (poly phenylene sulfide) resin, and a Flexible printed circuit 2 is used as means that supplies an electric signal. Accompanying with thinning of optical disk drive device, connectors cannot be used due to height limitations. Therefore, the Flexible printed circuit 2 is structured into an integral form to extend to a portion 8 thereof, which is inserted into a connector of a drive side.
FIG. 10 shows a state, in which an optical pickup device is assembled into an optical disk drive device. An optical pickup device body 1 has an objective lens 5 facing upwardly and the lens 5 is opposed to an optical disk (not shown) through a notched portion of a drive cover 9. The optical pickup device performs information reading and writing while moving between an outer periphery and an inner periphery of the optical disk. All these parts are assembled into an optical disk drive device body 10 to provide a product.
In this manner, while a Flexible printed circuit used in a thin optical pickup is structured in an integral form, portions arranged on an inner side and an outer side of the flexible printed circuit are different from each other in performance required originally, and high density is emphasized on the inner side and flexibility is emphasized on the outer side. Hereupon, means of solution in the Flexible printed circuit 2 made into an integral form has been proposed to select a Flexible printed circuit, which has optimum performances for high density and flexibility, as a method that meets both performances required of a portion of the Flexible printed circuit to be fixed to an optical pickup device and a portion of the Flexible printed circuit to be inserted into the connector of the drive.
On the other hand, various parts cannot but be arranged at a high density in horizontal and vertical directions in a narrow optical pickup device, and therefore, a Flexible printed circuit serving as signal transmission is required to assume a complex configuration. This requires a divided structure for a Flexible printed circuit in terms of cost since necessary configurations obtained from a single original sheet cannot be increased in number and even a portion, for which a simple structure will do, is influenced by a portion, which takes longest time, because of different necessary processes according to portions.
Meantime, the optical pickup device shown in FIG. 8, or an optical disk drive device, into which a thin optical pickup device is assembled, is assembled through a plurality of complex processes. Therefore, there often arises a case in which the optical pickup device or the optical disk drive device is deemed as defective products due to dents, defects, etc. generated in the Flexible printed circuit during assembling process after a process, in which adjustment is accomplished on a laser diode, a photodetector, and various optical parts of the optical disk drive, is performed. In this respect, by adopting division of a Flexible printed circuit into a plural printed circuits and connection of Flexible printed circuits, an increase in yield of products and reduction in cost can be realized (see, for example, JP-A-2005-276263 and JP-A-2006-245514).
Because of a height limitation on an optical pickup, a connector proposed in JP-A-2006-310449 cannot be used for connection of two Flexible printed circuits, and so the printed circuits are connected to each other by means of soldering. In case of adopting division of a Flexible printed circuit and connection of Flexible printed circuits shown in FIG. 9A, when a conductor pattern of a first Flexible printed circuit and a conductor pattern of a second Flexible printed circuit are caused to face and overlap each other, the second Flexible printed circuit is made to define a back surface and a connector side contact 8 is reversed. Hereupon, as shown in FIG. 9B, the connector side contact 8 is directed upward by connecting the other end of the first Flexible printed circuit and the other end of the second Flexible printed circuit so as to have them facing and overlapping each other, and bending the connected ends of the Flexible printed circuits at 90° in a height direction (vertical direction) of the optical pickup device, or fixing the connected end of the first Flexible printed circuit and bending the connected end of the second Flexible printed circuit at 180°.
With the connected structure shown in FIG. 9B, however, stress is liable to be applied on the connection portions of the first and second Flexible printed circuits in a peel direction and a tendency of much decrease in joint strength is shown such that a connection portion 2-d in the connected structure shown in FIG. 9B has an average peel strength of at most 1.5 kgf as compared with an average shear strength of 3 kgf in a connection portion 2-c in the case where the Flexible printed circuits are caused to face and overlap each other as shown in FIG. 9A.
Further, many wires are arranged in a narrow location on a portion of the Flexible printed circuit, in which the Flexible printed circuit extends out of a cover element 4 from the optical pickup device and at which the Flexible printed circuit is dividable and the divided printed circuits are connectable with each other, and a grounding wire having a wide wiring width and signal wires having a narrow wiring width are mixed in the portion, but wires having a narrow wiring width tend to be one-sided. Therefore, wires having a narrow wiring width and a wiring pattern width of at most 100 μm are used as outermost wires in many cases, and in case where the division of the Flexible printed circuit and connection of Flexible printed circuits is employed, a structure of the connected portion becomes such that peeling is liable to occur from an end of the wires having a narrow wiring width, that is, the outermost wires.
Electro solder plating tends to disperse much in thickness depending upon a wiring width. In the case where wires having a narrow wiring width and wires having a large wiring width exist as is in a Flexible printed circuit to be used in an optical pickup device, the dispersion of the plating is much and wires having a narrow width tends to be small in thickness of the electro solder plating as compared with wires having a large width.
On the other hand, when soldering is used to connect Flexible printed circuits, in order to remove a Flexible printed circuit which is in bad order from connection portions of Flexible printed circuits and connect a fresh Flexible printed circuit to the connection portions, there is adopted a method of reheating and melting the solder connection portions to remove the Flexible printed circuit in bad order. In such method, molten solder is moved to the Flexible printed circuit in bad order. Accordingly, it is hard to ensure the quantity of solder required for connection to the Flexible printed circuit in good order and fixed to an optical pickup body and repair connection is difficult.
From the above, a structure readily enabling reinforcement of connection portions and repair connection is needed when a Flexible printed circuit is divided and the divided Flexible printed circuits are connected.